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By Victor F. Hollister

Skam deposits considered as porphyry copper deposits have been classified into three basic prospecting models: (I) the skam deposit associated with a mineralized intrusive (Pima-Mission), (2) the deposit associated with a barren igneous stock (Ertsberg), and (3) mineralized rock that seems to have no clear association with apluton (Phoenix). Pima-Mission, Christmas, and many other copper-bearing skarns developed in carbonate sequences near mineralized intrusives form an important part of the deposit. Historically, copper derived from the mineralized intrusion accounts for less than half of the metal produced by most porphyry mines, as most mineralization occurs in the intruded rocks. Skam mineralization is an important part of wall-rock metal deposition, because carbonate sequences are preferentially replaced by sulfide and skarn minerals. Exploration for skam mineralization is an important phase of porphyry copper exploration. Impure carbonate beds can become better host rocks for skam deposits than pure carbonates, and these in particular should be included in porphyry-exploration programs if the impure strata are cut by the stock. Skam deposits can also form near stocks that are barren of sulfide. In this model, the two best ore guides are strata favorable for mineralization (usually impure carbonate beds) and the intrusive contact. Faults can also act as important ore controls. Some skarn deposits form that have no clear genetic connection with a stock, although intrusive rocks are known in the district. In such cases, the best ore guides are strata and district-wide faulting. Dikes and sills are also common and mineralization can locally prefer their contacts even though the igneous rocks are barren. Skam minerals are influenced by the chemical composition of the carbonate. Forsterite, brucite, tremolite, and talc are common in skams developed in dolomitic beds. Skams derived from calcic beds often contain wollastonite, calcite, stilbite, or idocrase. Diopside, however, is a common accompaniment of copper sulfide in skam regardless of the original composition of the carbonates. Tremolite and possibly other amphiboles and chlorite can occur significantly in the zinc-lead portion of skams. Gamets occur in magnetite, copper, and zinc-lead zones of skams, but are not as diagnostic as diopside for the copper zone or tremolite for the zinc-lead zone. A general desciption of skam-deposit mineralogy can be used to construct prospecting models of porphyry copper skams. An abstract of such a description follows.

Jan 1, 1991

By E. De Souza, J. F. Archibald

"Many underground mines use cemented backfill to mitigate environmental effects associated with tailings disposal. The large energy needs associated with mine backfilling and cement production operations create significant CO2 and Greenhouse Gas Emissions. This paper introduces post-consumer glass as an alternate, equally effective and lower cost binder agent strategy for cement in backfill that may be implemented to assist in reducing solid waste production, lowering energy costs, and restricting Greenhouse Gas Emissions. Extensive engineering testing, consisting of pipe flow loop tests and strength tests, has been implemented in order to demonstrate the technical feasibility of process integration within industry. An economic analysis has demonstrated that glass is competitive in cost relative to cement and a socioeconomic study has further indicated that the utilization of glass in mine backfill would create a new market for waste glass that requires less processing and reduces costs."

Jan 1, 2005

PolyMet Mining is developing the NorthMet property near Duluth, MN. Laboratory investigations have led to the development of the Platsol process to dissolve in one step the base metals (copper and nickel) as well as the gold and platinum group metals (PGM). To complete the prefeasibility study, a fully integrated, 10-day pilot plant trial was undertaken. The trial consisted of high-temperature (>220ºC or >428ºF) pressure oxidation in the presence of 5 to 10 g/L chloride (the Platsol process). This was followed by solid/liquid separation, gold plus PGM recovery from solution, conventional copper solvent extractions/electrowinning (SX/EW) and recycling of the copper raffinate to the autoclave. The concentrate tested during the trial period was a NorthMet bulk flotation concentrate. It assayed 14.7% Cu, 3.05% Ni, 0.14% Co, 26.7% S, 1.4 g/t (0.041 oz/st) Au, 2.2 g/t (0.064 oz/st) Pt and 9.9 g/t (0.289 oz/st) Pd Laboratory results were confirmed and, with minor adjustments of the laboratory Platsol conditions, the following leach extractions were obtained during the pilot plant trial: 99.6% Cu, 98.9% Ni, 96% Co, 94.6% Pd, 96 % Pt and 89.4 % Au.

Jan 1, 2003

By W. J. Deutsch, W. J. Martin, R. J. Serne

At the termination of mining, the quality of ground water in the ore-zone aquifer must be returned to a condition predetermined by the permitting agency. To immobilize the redox-sensitive elements (e.g., uranium, arsenic, selenium, molybdenum), it has been suggested that a reducing agent be circulated through the leached ore zone. We have conducted laboratory experiments to test the ability of sodium sulfide as such a reducing agent. Sodium sulfide lowered the redox potential of the effluent such that insoluble minerals containing the redox-sensitive elements should be stable. The uranium concentration of the solution decreased by more than three orders of magnitude. In column experiments, by the time 10 pore volumes of the sulfide solution had flowed through, sulfide minerals were forming. The experimental results indicate that the addition of sodium sulfide should cause chemical reduction of the leached sediments, thereby producing long-term stability of the ground-water/sediment system.

Jan 1, 1988

By G. Pan

A geostatistical approach is proposed for the design of infill drilling programs. The method is consisted of three major steps: developing geological favorability models, delineating mineralization and ore envelopes, and classifying reserves or resources. Geological modeling aims at developing favorable geological zones in which drilling is designed. Modeling mineralization and ore envelopes establishes criteria on potential blocks to be drilled. Top target blocks should be those included within ore envelopes. The framework of resource categories includes five types: probable reserves, indicated reserves, indicated resources, possible resources, and barren. Indicated reserves or resources are the top priority to be drilled for the definition of minable reserves. Possible resources may be considered as targets for further exploration. The algorithms involved in the analysis include indicator favorablity analysis, ordinary kriging, and indicator kriging. A case study presented here involves a gold deposit of Carlin type. The deposit was delineated by a sparse drilling program with 230 feet of average spacing. The infill drilling program designed by the new method suggests a significant reduction on the number of holes from a regular-grid infill drilling pattern.

Jan 1, 1995

By C. E. Jordan

Under its program of advancing minerals technology, the Federal Bureau of Mines has developed a laboratory apparatus for continuous separation of minerals according to their dielectric properties. The unit consists of a rotating wire grid drum electrode and a fixed curved wire screen electrode positioned 3 mm apart. By applying high voltage across the electrodes, which are immersed in a dielectric fluid medium, a high-gradient electric field is produced. The high-dielectric-constant minerals are attracted and conveyed through the separator by the rotating drum electrode, whereas the low-dielectric-constant minerals settle through the fixed electrode. In typical tests, a sample of Montana chromite ore containing 43 percent chromite was concentrated to 72 percent chromite with 90 percent recovery.

Jan 1, 1977

Little knowledge is available that considers the effects of continuous miner position on the possible respirable dust exposure of the remote mining machine operator. Such information could be very useful for increasing the awareness of the remote operator as to those parts of an extended cut that generate higher levels of respirable dust. This data could be used to develop guidelines for positioning the remote operator to reduce his potential exposure. This work details the effects of continuous miner position on dust levels measured on the machine and at the remote continuous miner operator location.

Jan 1, 1998

By Langtry E. Lynd

The titanium industry is based on the unique properties of titanium dioxide and titanium metal. Because of its whiteness, high refractive index and resulting light scattering ability, titanium dioxide in its two main allotropic forms, rutile and anatase, is the predominant white pigment for paints, paper, plastics, rubber, and various other materials. Titanium metal, because of its high strength/weight ratio and resistance to corrosion, is widely used for aircraft, both in airframes and engines, for powerplant surface condensers, and a wide variety of chemical processing and handling equipment. U.S. production of titanium dioxide pigment in 1979 was about 658,000 tons - 2/, valued at about $770 million. Net shipments of titanium mill products were around 19,000 tons, worth about $380 million. These two major uses account for over 96% of domestic titanium consumption. The third largest application, the use of rutile for coating welding rods, required about 9,500 tons of rutile concentrate, worth about $4 million. Other applications of titanium-bearing raw materials include the manufacture of titanium carbides, ceramics, and chemicals, and the recently developed use of ilmenite as a substitute for barite in well-drilling muds.

Jan 1, 1980

By S. Dessureault

Integrated information technology infrastructure is the linking of data across various applications throughout a business to gain further data-driven improvement opportunities. Decision support systems (DSS) are the various improvement opportunities that facilitate decision making for a potential optimal outcome. Integrating tera-bytes of data spread throughout a business is complex. There are tools to facilitate the development of such data-driven DSS. This paper analyzes the various tools that may facilitate the development of complex data-driven decision support systems, namely; information models, business models, data utilization model, and testing environments. A case study is presented to demonstrate how these tools facilitated the development of an automated activity-based budgeting DSS at a large-scale underground mining complex.

Jan 1, 2004

By Alexander N. Winchell

The cities of St. Paul and Minneapolis are located side by side on a double loop in the Mississippi River near the eastern boundary of Minnesota. Both cities lie on both sides 'of the Mississippi River, which in this region describes an S-shaped curve. The two cities together have a population of over 600,000 people, gathered in an area which has grown to be a single urban district inasmuch as the two cities have expanded until they occupy all the territory formerly between them, though the business centers are ten miles apart. St. Paul is located at the head of navigation on the Mississippi River and Minneapolis, farther upstream, at the Falls of St. Anthony. A recent water¬power development below the Falls of St. Anthony, constructed by the Federal Government, has at the same time made possible navigation to the foot of St. Anthony Falls through a lock around the dam which replaces the former rapids. Minneapolis, in 1920, had a population of 380,000 people, and St. Paul, 235,000. The two cities occupy land at an elevation of 700 to 900 feet above sea level. The average elevation is slightly less at St. Paul. Minneapolis has nearly 4,000 acres of parks and park¬ways, while St. Paul has nearly 2,000.

Jan 1, 1920

By Otis M. Clarke

The 34th Forum on the Geology of Industrial Minerals gave members a chance to see the geology of various stone and ore deposits displayed graphically in quarry walls and also provided an opportunity to hear and see first-rate papers and posters on the geology of industrial minerals. Also, some field trips passed through areas of spectacular scenery. As a bonus, participants saw scenic mines, some of which are "pretty as a picture." Watercolor paintings prove it. At the Oklahoma Forum, the writer displayed a number of paintings of mines and other landscapes seen during previous Forum trips. These paintings and this brief article are part of a crusade to prove that some mines and geologic vistas are scenic wonders and belong in our visual heritage. It is a plea to save some of our best geologic exposures for future geologists, tourists, and artists.

Jan 1, 1999

By Gerald C. Smith

Carlin Gold Mining Company is a wholly owned subsidiary of Newmont Mining Corporation and is located 76 kilometers north west of Elko, Nevada. Multiple bench open pit mining methods are being used to mine 24.5 Mt of ore and waste per year. Mining started in 1964 and up through 1983 Carlin has mined 138 Mt of ore and waste and has milled 13.8 Mt of ore. Selective mining of carbonaceous and oxide ores together with a good grade control program have been key factors in the success of the operation. This paper will present the raining methods and the mining equipment being utilized to make Carlin Gold Mining Company a very profitable operation while mining and milling low-grade gold ore.

Jan 1, 1985

By David Humphreys

Assumptions about future commodity prices need to be made with close regard to the purposes for which they are being used. Prices generated for financial planning or trading purposes are unlikely to be suitable for the longer run purposes of project evaluation and reserve estimation. In this latter context, price assumptions need to be realistic, stable and rooted in a rigorous fundamental analysis of long run industry drivers. Amongst the factors to be considered in such analysis are price history, production costs and structural dynamics. It is also important that prices adopted are consistent with other information being used by a company in its decision-making.

Jan 1, 2003

By Pierre Longtin

"Replacing the aging roadway access to the iconic Golden Gate Bridge, thereby ensuring traffic safety and robustness in case of seismic occurrences, provided an opportunity for major design improvements as well as the development of a parkway that would include the construction of four new tunnels. With an eye to the future, the Doyle Drive replacement project aimed to meet the highest standards for environmental stewardship beyond regulatory requirements. Understanding that lighting equipment is the tunnel‘s subsystem that uses the most energy, the operator was looking for a sustainable solution to light the tunnels. An Intelligent Lighting Control System (ILCS), designed specifically for road tunnels, was acquired to individually control the almost 2000 luminaires lighting the four tunnels. This paper will show the results in terms of energy and operational savings generated over the nine months of operation between the commissioning and the conference in April 2016. INTRODUCTION Electrical & mechanical (E&M) equipment represents an average of 10 % of a tunnel total construction cost. Once the civil infrastructure completed, E&M equipment drives the main part of the expense during a tunnel useful life. Table 1 below describes the impact of various types of energy consumption and their cost impact in tunnels of less than 500 m. It is clear that lighting is the sub-system that requires the most energy. A good lighting strategy is the key to reducing energy consumption due to lighting and a viable solution that will bring important savings in tunnel operations.With a price of $0.14/kWh in California and a planned increase between 3% and 6% per year during the period 2013-2040, the tunnel operators could not afford to overlit the tunnels—particularly when they have to operate it for the next 30 years. However, they also need to maintain the right lighting level to ensure driver safety all the time. The Presidio Parkway project includes the Battery tunnels, which are 240 m (790 feet) and 230 m (750 feet) in length, and the Main Post tunnels, which are 280 m (920 feet) and 315 m (1030 feet) in length."

Jan 1, 2016

By Thomas D. Kaufmann

Whether pursuing hedging or speculative strategies, gold miners can increase sales revenues 1 % to 6% by constantly pricing production forward. Unlike other commodities, gold futures prices are consistently higher than spot prices. A Colorado School of Mines study showed theoretically and empirically that in the 15 years since the price of gold was released from government control, the forward price for gold has been higher than the current price almost 100% of the time. The reason why Metal traders know that holders of metal earn a bonus selling forward when the metal is in "contango." "Contango" is a mysterious word that crept into the trading vocabulary a century ago. It designates a situation when the price of a metal on the futures markets is higher than the price in the immediate or spot market. If the spectrum of spot and futures prices remains static over time, the forward seller who has contracted at a higher than spot price can make a profit equal to the contango by redeeming his commitment at the lower spot price when the contract matures. Consequently, when a seller in a contango market hedges, he makes a profit on the transaction in addition to avoiding a price change risk. On the other hand, buyers of the metal who hedge in a contango situation will sustain a loss equal to the contango. Producers of gold, however, are sellers of gold. For most metals and oil, there is no inherent reason why futures prices should be higher than present prices. Buyers and sellers decide that the price of the commodity will be lower or higher than present values for a variety of reasons.

Jan 1, 1991

By A. E. Raddatz

The U.S. Department of the Interior, Bureau of Mines, is investigating methods for recovering tungsten from domestic resources. A calcine-quench-leach (CQL) technique was developed for the extraction of tungsten from the Golconda, Nevada, hot springs ores. The deposit contains disseminated tungsten, which cannot be beneficiated by conventional techniques and must be treated by hydrometallurgical methods. The CQL procedure consists of calcining the ore at 900° C for 3 hr, quenching in a solution containing 1.5 parts of NazCO3 and 1.5 parts of NaOH per part of WO3 in the ore and at a solution- to-ore ratio of 3 to 1, leaching at 200° C and at 250 psig for 3 hr, and filtering and washing the residue. A series of closed-circuit batch tests showed that 92 pct of the tungsten was extracted from a sample containing 2.32 pct WO3. The pregnant solution contained 11 q of W03/1.

Jan 1, 1982

By N. Arbiter

Introduction The theoretical analysis of tumbling mill energetics and performance has largely neglected mill dimensionality, and, in particular, the importance of the length/diameter (L/D) ratio. This is in spite of the fact that practice varies substantially: geographically, for semi-autogenous and autogenous mills, as between North America and South Africa/Scandinavia, and historically, for overflow ball mills, for which the L/D ratio has increased significantly from the earliest small mills to the largest mills currently. The present study is concerned primarily with the influence of the L/D ratio on the design and operation of overflow ball mills, on the occurrence of the overload phenomenon, and on the limits, if any, it may impose on mill capacities because of critical pulp axial velocity limits. It will be shown that the shape factor is of major importance in this area and that its adjustment to the extent that this is practical should remove the diameter limitations previously postulated for this mill type. Dimensionality in mill design Ball mill shape factors in the period prior to 1927 (Taggart, 1927) averaged 1.1/1 for 29 center discharge mills and 1.0/1 for 30 peripheral discharge mills. With the resumption of new plant construction after the 1930s depression, the Morenci concentrator continued the 1/1 ratio with its 3.1 x 3.1 m (10 x 10 ft) mills. The ratio was increased progressively from then on, reaching 1.6 and 1.8/1 for the largest overflow mills currently. As shown recently (Arbiter, 1989), this is in sharp contrast to autogenous and SAG mill shapes, for which the ratio averages 0.4 in North America. On the other hand, South African practice, starting at the turn of the century with autogenous mills having 4/1 ratios, moved toward 1/1 until recently, when a 2.5/ 1 ratio mill was installed. The reasons given for such divergent practice for mill shape factors are in some respects contradictory and generally inconclusive. The most complete discussion from a practical viewpoint (Dor and Bassarear, 1982) is limited to primary SAG and autogenous mills. Considerations of ball mill dimensionality have had a twofold direction. On the one hand, it has been argued that ball mill efficiencies should increase with increasing diameter and that the specific energy for a particular grind should be reduced accordingly. An inadvertent test of this idea at the Bougainville operation (Burns and Erskine, 1983) resulted in drastic underpowering, which led to failure to reach design capacity until additional mills were installed. This can be taken as strong evidence against any increase in efficiency with diameter. In another direction, it has been argued (Arbiter and Harris, 1982, 1983) that there is a limit to ball mill diameters because of the demonstrable limit to axial flow velocities evident in the overload phenomenon, which as a fact is incontrovertible. But that it places a limit on mill diameters overlooks the evidence given below that appropriate variation in the L/D ratio will permit major increases in diameter, limited only by constructional or economic factors. The present study was directed toward quantifying the overload phenomenon through examination of the influence of mill dimensionality variation and mill operating variables on its occurrence. It is shown that varying the operating conditions, specifically the load fraction and the fraction critical speed, can reduce the risk of overload for existing operations; while appropriate decreases in the L/D ratio can minimize the risk in the design of new circuits. Ball mill overload Ball mill overload is a consequence of the approach to a critical velocity with increasing feed rates or circulating loads. Although the effect has been known for over 50 years, there have been no previous attempts to quantify it. The following description of the ball mill as a flow system is the preliminary to a quantitative analysis: 1) In the absence of a ball load, axial flow of pulp through a mill resembles open channel flow, except for disturbances near the shell due to shell/lifter rotation. 2) For a given ball load (Lf), the void fraction available for pulp hold-up (H) for the ascending portion of the load is approximately 0.4 Lf. In the descending portion, it is greater than this and increases with fraction critical speed (Fc) because of load expansion. 3) Increasing the feed rate increases pulp hold-up and progressively fills the available void space. At a critical flow rate, which depends on system geometry, hydraulic head and pulp rheology, void filling reaches its limit; a pool forms rapidly and fills available space outside the ball load and up to the overflow level. Prior to this, pulp discharges mainly along the ascending rim of the overflow. 4) For a small mill (Lo et al., 1990), it has been shown that with increasing feed rates the critical filling is at or near 50% of the mill volume. Power drops rapidly when this level is reached, as required by the torque formula. 5) The transition to overload is associated with the following phenomena: a) The decrease in power draw. b) Damping of mill sound. c) Reduced comminution of coarser feed sizes, probably due to reduced direct impact in the presence of a pool. d) Increased circulating loads, which further intensify the overload, and increased density of cyclone underflows, which can lead to roping. e) Conditions beyond overload are not known because feed rates are not delibelrately increased beyond this point. f) The existence of the phenomenon limits the capacity of a mill with a fixed set of operating conditions and can prevent the balancing of hard ore feed rate decreases by increases in soft ore rates.

Jan 1, 1992

By H. C. Verakis

Permanent ventilation controls such as stoppings, overcasts, and undercasts for use in coal mines are required to meet MSHA’s safety standards for fire endurance and flexural strength. Due to technological advances in materials and their design for use as ventilation controls, an engineering program was established to evaluate newer or “nontraditional” ventilation controls. The program is intended to assist manufacturers, enforcement personnel and mine operators in determining if “nontraditional” ventilation controls, for example plastic membrane construction and lightweight block, meet the prescribed safety standards. The program is presented with a description of required tests and examples of products evaluated.

Jan 1, 2003

By Stig Eriksson

In Switzerland two major railway systems as shown below in Figure 1 has recently been completed or is under construction: ¦Lötschberg, south of Bern which was commissioned in 2007 ¦Gotthard, south of Zurich which is scheduled to be commissioned in 2016The aim is to increase the transport capacity of the railway system and to transfer more transport of goods to the railway by offering transport of trailers and lorries on the new railway systems. It will have a positive environmental impact but also improve the congested traffic situation of the highways in north-south directionThe Gotthard tunnel is totally 57 km (35 mile) long and the Lötschberg tunnel is 35 km (22 mile) long. Both tunnel systems consist of two parallel single track tunnels connected with cross tunnels at every 333 m (1 093 ft). Additionally there are cross-over tunnels and caverns for installations and operation. In the Lötschberg tunnel, the majority of the excavation has been by Drill & Blast and in Gotthard tunnel the major part is being excavated by TBM.

By M. H. Foroughi

This paper discusses the effects of seam inclination and lateral stresses on the stress distribution in pillars in inclined coal seams. The average pillar stress is a function of the overburden weight, the mine depth, the effective extraction ratio and the angle of seam inclination. Normal and shear stresses in the pillar are computed by numerical modeling. In medium dipping seams, leaving a pillar with its axis normal to the stratification causes a shearing stress concentration in the top and bottom corners of the pillar. This results in the pillar possibly becoming less stable in comparison to pillars in horizontal coal seams. Therefore, to reduce the stresses, it may be necessary to leave the pillar at an angle of b deviated from the normal axis to stratification. A mathematically approximate formula for determining b is proposed, and the results are confirmed by numerical modeling.

Jan 1, 1998